This invention relates to denitrating catalysts for use in a reaction in which nitrogen oxides (NO.sub.x) in exhaust gases are selectively catalytically reduced with NH.sub.3, and to a process for producing the catalysts.
Many processes for treating NO.sub.x in exhaust gases have already been proposed. Among these processes, the denitration process is most feasible in which nitrogen oxides are selectively catalytically reduced to harmless N.sub.2 at a specified temperature with NH.sub.3 in the presence of a catalyst. Although many catalysts have also been proposed for use in this process, they still remain to be improved. We prepared a catalyst from the porous metal material disclosed in U.S. Pat. No. 4,040,981 by immersing a catalyst base of the metal material in a silica-containing coating bath and drying the catalyst base to form a porous silica coating thereon. We found that the catalyst has high mechanical strength and retains sustained stable activity free of poisoining as by KCl. This invention relates to improvements in this catalyst.